[NTLUG:Discuss] Microphone

[Steve Baker]

> Kyle_Davenport at compusa.com wrote:
> >
> > I use gmix.  There's a mixer setting on it which I guess controls /dev/mixer.
> > There's a nice utility in Redhat called MAKEDEV which creates all the audio
> > devices.   It depends on your particular card's driver which device, dsp,
> audio,
> > dsp1, or dsp2, you are using for recording and playing.  I can cat /dev/audio
> or
> > /dev/dsp and watch signals go thru it when I talk into the mike.
> >
> Using 'record' from a terminal I can see activity when I talk into the
> mic. I just don't have any sound when I play back the file. Doing the
> cat commands you recommended I see gibberish go across the screen.

In the hardware behind the audio mixer, there is a switch that
selects which input actually gets fed into the recording software.
(It could be the Microphone, the Line input, the phone, the CD
player...maybe others).

On my sound card, you can have the mic plugged in and turned on
and when you talk into it, you can hear your voice coming out
of the computer's speakers.  The Mic-volume on the mixer changes
the volume just as you'd expect - but recording the sound using
something like krecord produces files containing noise - but nothing
from the microphone.  That sounds like a fair characterization of
your problem.

The problem is that unless the audio mixer has the microphone selected
as the record input, none of that sound data makes it into the CPU.

The exact solution depends on which mixer control program you use,
some have specific buttons...I use kmix - and it makes the 'line'
input be the record input by default - you have to right-click on
the Mic slider and select 'RecSource' to make the microphone be the
input device.

If you have that wrong, then just looking at the numbers in the files
produced by the record program - or cat'ing the data to the screen
won't tell you very much because the stray noise coming from the
line input will be enough to show 'interesting' non-zero data.

That data might even appear to change when you talk into the
mic - there is a certain amount of cross-talk in any audio
system - and that might well be enough to make the numbers
change a teeny-tiny bit.

It took me *ages* to figure this out when it fist happened to me!
The 'right-click on the mic slider' trick for kmix *sucks* as a
user interface for the uninitiated!

-- 
Steve Baker                  http://web2.airmail.net/sjbaker1
sjbaker1 at airmail.net (home)  http://www.woodsoup.org/~sbaker
sjbaker at hti.com      (work)